It is known in wet assay analyzers to provide cartridges of reagents to a rotor, by inserting them along a radius of the rotor where they are processed with the other cartridges likewise inserted. Examples, are shown in, e.g., U.S. Pat. Nos. 5,075,082 and 5,219,526. However, previous constructions have either required the insertion into the rotor to be manual, as in the '082 patent, or to be done by using a pusher that has to be withdrawn afterwards before the rotor can rotate, the pusher being effective only to load a cartridge, and not to unload it, as shown in the '526 patent.
Therefore, prior to this invention there has been a need for automated means for insertion of reagent cartridges into a rotor that is versatile enough to both a) remain inside the rotor enclosure during rotor rotation and b) act to withdraw a spent cartridge as well as insert a new one.